JP2014024097A - Regeneration method of casting sand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of regeneration sand, capable of sufficiently removing fine powder stuck to a surface of casting sand.SOLUTION: The regeneration method of the casting sand collected by separating a sand mold used for casting, comprises a roasting-baking process (a step S5) for burning down an organic substance stuck to the casting sand by roasting-baking the casting sand, a first polishing process (a step S7) of shaving off from the surface a coating film including hematite having magnetism finally formed on a surface of the casting sand by executing the roasting-baking process and a second polishing process (a step S8) of polishing the surface of the casting sand of shaving off the coating film from the surface in a casing 51 by grinding capacity lower than grinding capacity in the first polishing process, and the second polishing process is a process of discharging the fine powder to the casing outside by wind power by peeling off the fine powder stuck to the surface of the casting sand of which the coating film is shaved off from the surface by the first polishing process.

Description

  The present invention relates to a method for recycling foundry sand recovered by releasing a sand mold used for casting.

  The casting sand used for the main mold and core formed by sand mold is processed by a predetermined recycling method for the purpose of reducing waste and protecting resources such as silica sand, etc. Used for materials.

  Various methods, such as a wet regeneration method, a dry regeneration method, a roasting regeneration method, and a combination of a roasting regeneration method and a dry regeneration method, have been proposed and implemented as a method for reclaiming foundry sand.

  Among these regeneration methods, the applicants of the present application have proposed a method for regenerating foundry sand by combining a roasting regeneration method and a dry regeneration method (see Patent Document 1). The method for reclaiming foundry sand described in Patent Document 1 is that after performing a predetermined pretreatment process such as drying and removal of foreign matter on the foundry sand recovered by separating the green sand mold used for casting, A roasting process is performed in which the sand is roasted to burn off organic substances such as resin and seacoal adhering to the foundry sand. Next, a cooling step is performed to cool the foundry sand to a predetermined temperature, and then a polishing step is performed in which the coating formed on the surface of the foundry sand by the roasting step is scraped with a grindstone. This coating is called an auritic, and is mainly a bentonite sintered product formed into a porous glass-like substance, and contains magnetic hematite. In addition, the auritic may contain a core binder, a residual component of seacoal, and the like. After the polishing step, a magnetic separation step is performed in which the foundry sand that adheres firmly and remains on the surface and the auritic scraped from the foundry sand are removed using magnetic force.

  According to the method for reclaiming foundry sand described in Patent Document 1, it is possible to remove from the foundry sand the auristic formed on the surface of the foundry sand by the roasting process.

JP-A-6-170485

  However, in the method of reclaiming the foundry sand described in Patent Document 1, although the auristic can be removed from the foundry sand, when the auristic is scraped off in the polishing process, the scraped auritic fine powder is formed from the foundry sand. It will adhere to the surface. This fine powder is an alkaline powder having a central particle size of 20 μm or less mainly composed of magnetic hematite or bentonite, and a mixture of magnetic powder and non-magnetic powder. For this reason, the fine powder having magnetism can be removed to some extent in the subsequent magnetic separation process, but the actual situation is that the fine powder having no magnetism cannot be removed.

  By the way, in the shell mold method, the cold box method, or the self-hardening mold manufacturing method, a phenol resin, a phenol urethane resin, an alkali phenol resin, or the like is added as a binder. When reclaimed sand is used in the manufacturing method of these molds, if fine powder adheres to the surface of the reclaimed sand, a portion where the phenol resin added by the fine powder does not come into contact with the reclaimed sand is generated. Etc. The wettability (affinity) such as becomes worse. As a result, the adhesive strength of a phenol resin or the like as a binder may be reduced, and the strength of the core may be insufficient. In particular, binders such as phenol urethane resin added to the cold box method are very reactive and react at the interface when they come into contact with alkaline fine powder. For this reason, if the fine powder adheres to the surface of the regenerated sand, when the phenol urethane resin or the like is added to the regenerated sand, the added binder such as the phenol urethane resin reacts and cures at that time. There is a problem that the pot life will be shortened. The pot life as used herein refers to the time from kneading of a molding sand to which a binder or various additives are added until molding can be performed.

  An object of this invention is to provide the manufacturing method of the regenerated sand which can fully remove the fine powder adhering to the surface of foundry sand in view of the said situation.

The method for reclaiming the foundry sand of the present invention that solves the above-mentioned object is a method for reclaiming the foundry sand recovered by separating the sand mold used for casting,
Roasting step of roasting the foundry sand and burning off the organic matter adhering to the foundry sand;
A first polishing step of scraping from the surface a coating containing magnetic hematite that has been formed on the surface of the foundry sand by performing the roasting step;
A second polishing step in which the surface of the foundry sand from which the coating has been scraped off from the surface is polished in a housing with a grinding ability lower than the grinding ability in the first polishing step;
The second polishing step is a step of peeling fine powder adhering to the surface of the foundry sand from which the coating has been removed by the first polishing step from the surface, and discharging the fine powder out of the casing by wind force. It is characterized by being.

  The term “polishing” as used herein refers to a general term for grinding and polishing, wherein the first polishing step is mainly a grinding step, and the second polishing step may be a finishing step.

  In the first polishing step, polishing is performed using a grindstone (for example, a solidified abrasive grain) as a polishing tool, and in the second polishing step, a polishing tool other than a grindstone (for example, ceramic molding) is used. Polishing may be performed using the body. The polishing tool used in the first polishing step is preferably harder than the polishing tool used in the second polishing step.

  Further, the foundry sand may be a mixture of foundry sand collected by separating the core used for casting. The core may be a core manufactured by a shell mold method, a cold box method, or a self-hardening mold manufacturing method.

  According to the method for reclaiming foundry sand of the present invention, in the second polishing step, the surface of the foundry sand is polished with a grinding ability lower than the grinding ability in the first polishing step, thereby suppressing fine powder generated by polishing. Meanwhile, fine powder can be efficiently peeled off from the surface of the foundry sand. In addition, since the second polishing process is a process in which fine powder adhering to the surface is peeled off from the surface of the foundry sand, and this fine powder is discharged out of the casing by wind force, the fine powder peeled off from the surface of the foundry sand by polishing is removed. It is possible to prevent reattachment to the foundry sand.

  Further, the method for reclaiming foundry sand according to the present invention includes a magnetic separation step for removing the foundry sand in which the film remains on the surface using a magnetic force even though the first polishing step is performed. It is preferable.

  Here, the magnetic separation process may be performed before the second polishing process or may be performed after the second polishing process as long as the first polishing process is performed. .

  By the magnetic separation process, the foundry sand with the coating film remaining on the surface can be removed. Moreover, when the fine powder which has magnetism remains on the surface of foundry sand, in this magnetic separation process, fine powder is removed using magnetic force.

  According to the method for reclaiming foundry sand of the present invention, fine powder adhering to the surface of the foundry sand can be sufficiently removed.

It is a flowchart which shows each process of the reproduction | regeneration method of the foundry sand which is embodiment of this invention. It is a front view which shows the internal structure of the 1st grinding | polishing machine used by the 1st grinding | polishing process (step S7) shown in FIG. It is a front view which shows the internal structure of the 2nd grinding machine used by the 2nd grinding | polishing process (step S8) shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a flowchart showing a manufacturing process of a casting sand recycling method according to an embodiment of the present invention.

  As shown in FIG. 1, in the method for reclaiming foundry sand, the foundry sand obtained by separating the sand mold used for casting is collected and accommodated in a hopper (step S1). The recovered foundry sand mainly corresponds to foundry sand in which the added core sand overflowed in the fresh sand mold casting method using the main mold of the fresh sand mold. Core sand is foundry sand that forms a core manufactured by a shell mold method, a cold box method, a self-hardening mold manufacturing method, or the like. For this reason, the recovered foundry sand is a mixture of foundry sand forming the green sand mold and foundry sand forming the core manufactured by the shell mold method or the like. In addition, bentonite contained in the green sand mold and additives such as seacoal remain in the recovered foundry sand, and phenol resin, which is a binder for cores manufactured by the shell mold method, etc. also remains. ing. Further, the recovered foundry sand may be mixed with metal impurities such as core metal, nails, wire used in the sand mold, swarf generated during pouring, or steel shot.

  The recovered foundry sand is conveyed from the hopper to the magnetic separator, and the first magnetic separation process is performed by the magnetic separator (step S2). In the first magnetic separation process, the metal impurities are removed from the recovered foundry sand. The foundry sand from which the metal impurities have been removed is conveyed to a dryer and a drying process is performed (step S3). In the drying process, water contained in the foundry sand is removed, and part of seacoal, phenol resin, and the like are also removed. In addition, a rotary dryer (rotary continuous dryer) is used for the dryer. The foundry sand that has been subjected to the drying process is transported to a sieving machine, and a sieving process is performed (step S4). In the sieving step, massive casting sand is separated and impurities are removed. The separated massive foundry sand is pulverized by a pulverizer or the like and then returned to the foundry sand subjected to the sieving step.

  The foundry sand that has been subjected to the sieving process is transported to a roasting furnace, and the roasting process is performed (step S5). In the roasting step, the foundry sand is fired at about 700 ° C., and the resin such as phenol resin and the organic components such as seacoal contained in the foundry sand are burned off. In addition, the loss on ignition (ignition loss) such as resin and seacoal contained in the foundry sand before performing the roasting process is generally 3 to 4%, but by performing the roasting process The ignition loss of foundry sand is reduced to 0.5% or less, preferably 0.2% or less. Moreover, if a roasting process is implemented, an otic will be formed in the surface of foundry sand. This auritic is mainly a sintered product of bentonite which is a porous glassy material, and contains hematite having magnetism. In other words, this auritic corresponds to the coating film containing hematite having magnetism according to the present invention.

  The foundry sand subjected to the roasting process is transported to a cooling device, and after performing a cooling process (step S6) in which air is cooled while sprinkling water, it is transported to a first polishing machine and performs a first polishing process. (Step S7). A 1st grinding | polishing process is demonstrated using FIG.

  FIG. 2 is a front view showing the internal structure of the first polishing machine used in the first polishing step (step S7) shown in FIG.

  If casting sand with a surface of Auritic is used as the core material as reclaimed sand, phenolic resin, which is a binder, is adsorbed to the pores formed on the surface of the porous Auotic. As a result, the wettability (affinity) of the phenol resin or the like with respect to the recycled sand is deteriorated. As a result, poor curing of a phenol resin or the like as a binder may occur and the core strength may be insufficient. For this reason, the auristic is removed from the surface of the foundry sand by the first polishing step.

  As shown in FIG. 2, the first polishing machine 3 includes a frame 31, a box-shaped main body 32 installed on the frame 31, a grindstone 33 disposed in the lower part of the main body 32, The hoisting drum 34 is disposed outside the grindstone 33.

  The grindstone 33 is a polishing tool in which abrasive grains such as alumina abrasive grains are hardened, and is formed in a cylindrical shape extending in a direction perpendicular to the paper surface in FIG. In addition, the grindstone 33 is good also as a structure which provides an alumina abrasive grain only in a cylindrical-shaped circumferential surface. Further, the grindstone 33 is rotated clockwise in FIG. 2 by a motor (not shown) around a rotation axis in a direction orthogonal to the paper surface in FIG.

  The scraping drum 34 has a cylindrical cylindrical portion 341 extending in a direction perpendicular to the paper surface in FIG. 2 and a plurality of scraping pieces 342 attached to the inner peripheral surface of the cylindrical portion 341. The scraping piece 342 is formed so that the tip thereof has a slight gap with the grindstone 33. Further, the scraping drum 34 is rotated counterclockwise in FIG. 2 by a motor (not shown) around a rotating shaft provided at the same position as the rotating shaft of the grindstone 33. As a result, the grindstone 33 and the scraping drum 34 rotate in opposite directions with a slight gap between the circumferential surface of the grindstone 33 and the tip of the scraping piece 342 in the scraping drum 34. The scraping drum 34 is rotated more slowly than the grindstone 33.

  The bottom portion 325 of the main body 32 is formed in a semi-cylindrical shape corresponding to the shape of the scraping drum 34, and a sand discharge port 325a is formed in the lowest portion of the bottom portion 325. An opening / closing device 324 for opening and closing the sand discharge port 325a is provided at the bottom 325 of the main body 32. Note that a sand receiving member 311 is provided in a portion of the underframe 31 below the sand discharge port 325a.

  On the side surface of the main body 32, a sand throwing portion 321 for throwing casting sand toward the scraping drum 34 is provided. In addition, air inlets 322 are provided on both side surfaces on the lower side of the main body 32, and exhaust ports 323 are provided on the upper side surface of the main body 32. The exhaust port 323 is connected to a dust collector (not shown).

  In order to perform the first polishing step using the first polishing machine 3, first, the grindstone 33 is rotated, and the scraping drum 34 is moved at a speed slower than that of the grindstone 33 and with the grindstone 33. Rotate in the opposite direction. Next, in a state where the opening / closing device 324 closes the sand discharge port 325a, the casting sand S is thrown into the scraping drum 34 from the sand throwing portion 321 and then a dust collector (not shown) is operated.

  The foundry sand S put in the scraping drum 34 moves toward the grindstone 33 as it is scraped up by the scraping piece 342 of the scraping drum 34, and is in contact with the grindstone 33 while being pushed by another foundry sand. It drops from a gap formed between the grindstone 33 and the tip of the scraping piece 342. The falling foundry sand S is again scraped up by the scraping piece 342, and the contact between the foundry sand S and the grindstone 33 is repeated. As a result, the sand of the foundry sand S can be ground away from the surface of the foundry sand S, which has been sufficiently ground and formed by performing the roasting process. Further, due to the suction action of a dust collector (not shown), an air flow from the intake port 322 to the exhaust port 323 is generated in the main body 32 as indicated by an arrow in FIG. For this reason, some of the olitic scraped off from the surface of the foundry sand S by grinding is collected by the dust collector from the exhaust port 323, but the remaining fine powder is electrostatically applied to the surface of the foundry sand S. It adheres by the action of etc.

  The grindstone 33 and the scraping drum 34 continue to rotate until the authetic is uniformly scraped from the cast sand S that has been thrown in. Then, the grindstone 33 and the scraping drum 34 are stopped from rotating, and the dust collector is also stopped. Next, the opening / closing device 324 is driven to open the sand discharge port 325 a, and the foundry sand S is discharged to the sand receiving member 311.

  The foundry sand that has been subjected to the first polishing step is conveyed to the second polishing machine, and the second polishing step shown in FIG. 1 is performed (step S8). The second polishing process will be described with reference to FIG.

  FIG. 3 is a front view showing the internal structure of the second polishing machine used in the second polishing step (step S8) shown in FIG.

  As shown in FIG. 3, the second polishing machine 5 includes a casing 51, two polishing drums 52 rotatably disposed inside the casing 51, a motor 53 that rotates the polishing drum 52, a casing A blower 54 for blowing air into the body 51 is provided.

  The casing 51 has a rectangular outer shape, and the inside thereof is partitioned into three regions in the vertical direction. The casing 51 includes a blower chamber 511, a polishing chamber 512, and a classification chamber 513 in order from the bottom. Is formed. A blower 54 is connected to the blower chamber 511. The polishing chamber 512 is a region where the foundry sand is polished and fine powder is peeled off from the surface of the foundry sand, and the classification chamber is a region where the foundry sand and fine powder are selected. A partition plate 511a is provided between the blower chamber 511 and the polishing chamber 512, and a plurality of blower pipes 511b protruding upward and penetrating in the vertical direction are formed on the partition plate 511a. The blower pipe 511 b is provided with a mesh member (not shown) so that the foundry sand S does not enter the blower chamber 511. A baffle plate 512a is provided between the polishing chamber 512 and the classification chamber 513, and a plurality of communication holes communicating with the polishing chamber 512 and the classification chamber 513 are provided in the baffle plate 512a.

  On the side surface of the casing 51, a sand throwing portion 514 for throwing the foundry sand S into the polishing chamber 512 is provided. A sand discharge port 515 is provided on the side surface of the casing 51, which faces the side surface of the casing 51 provided with the sand throwing portion 514. The sand discharge port 515 is formed obliquely downward from a position corresponding to the lower portion of the polishing chamber 512. An exhaust port 516 is provided on the upper surface of the housing 51, and the exhaust port 516 is connected to a dust collector (not shown).

  The polishing drum 52 corresponds to a polishing tool used in the second polishing step, and is composed of a ceramic molded body. The polishing drum 52 has a disk-shaped disc portion 521 and a cylindrical ring portion 522 formed on the outer periphery of the disc portion 521, and the cross section shown in FIG. Here, in the first polishing step, a grindstone 33 in which alumina abrasive grains are hardened is used as a polishing tool, and the grindstone 33 is harder than the polishing drum 52. In the polishing drum 52, the ring portion 522 may be formed of a ceramic molded body, and the disk portion 521 may be formed of another material. In this embodiment, two polishing drums 52 are provided, but one polishing drum 52 may be provided, or three or more polishing drums 52 may be provided.

  A rotating shaft 531 is connected to the drive shaft of the motor 53, and the polishing drum 52 is fixed to the rotating shaft 531 in a state where the rotating shaft 531 passes through the center of the disk portion 521.

  A second polishing process using the second polishing machine 5 will be described.

  First, casting sand is put into the polishing chamber 512 from the sand throwing unit 514, and then the motor 53 is operated to start the rotation of the polishing drum 52. The foundry sand S is continuously fed into the polishing chamber 512 from the sand throwing portion 514. Next, the blower 54 is operated to start blowing into the blower chamber 511, and a dust collector (not shown) is also operated. As a result, as shown by the arrows in FIG. 3, the air sent from the blower 54 to the blower chamber 511 is blown into the polishing chamber 512 from the blower pipe 511b and passes through the communication hole of the baffle plate 512a. After entering, the air further rises and is discharged out of the casing 51 through the exhaust port 516 and is collected by a dust collector (not shown).

  The foundry sand S in the polishing chamber 512 is blown up by the wind of the air blown from the blower pipe 511b and is also swept up by the rotation of the polishing drum 52, and flows in various directions while the foundry sands S collide with each other. . Further, the flowing casting sand S enters the polishing drum 52, and the casting sand S collides more intensely with the rotation of the polishing drum 52, and also contacts the inner peripheral surface of the ring portion 522 in the polishing drum 52. Is polished. Since the foundry sand S collides with each other and is brought into contact with the ring portion 522 of the polishing drum 52 and polished, the attached fine powder can be sufficiently peeled from the surface of the foundry sand S. The ring portion 522 of the polishing drum 52 is formed of a ceramic molded body, whereas the polishing tool in the first polishing step is a grindstone 33 in which alumina abrasive grains are hardened. For this reason, the grinding capability of the second polishing step is lower than the grinding capability of the first polishing step, and the finishing step is mainly performed in the second polishing step.

  Further, since the centrifugal force is generated by the rotation of the polishing drum 52 in the foundry sand S that has entered the polishing drum 52, it is scattered from the polishing drum 52 in various directions, and the baffle plates 512a and the casting sand S repeatedly collide with each other. It also collides with the wall surface of the polishing chamber 512. The fine powder adhering to the surface of the foundry sand S can be peeled off by the collision of these foundry sands S or the collision with the baffle 512a or the like.

  The fine powder peeled off from the surface of the foundry sand S is blown up into the classification chamber 513 through the communication hole of the baffle plate 512a by the wind of air rising in the polishing chamber 512 together with the relatively fine foundry sand. The fine powder blown into the classification chamber 513 is discharged out of the casing 51 through the exhaust port 516 and is collected by a dust collector (not shown). Thereby, it can prevent that fine powder adheres to the foundry sand S again. The foundry sand S blown into the classification chamber 513 falls into the polishing chamber 512 due to its own weight, and the polishing drum 52 is polished again.

  Further, the foundry sand S from which the fine powder adhering to the surface has been removed is sequentially discharged from the sand discharge port 515. The amount of foundry sand S discharged from the sand discharge port 515 is proportional to the amount of foundry sand S charged from the sand throwing unit 514, and if the amount of foundry sand S thrown from the sand throwing unit 514 is increased. As the number increases, the amount of foundry sand S discharged from the sand discharge port 515 increases, and the time for which the foundry sand S stays in the polishing chamber 512 is shortened. For this reason, the time which implements a 2nd grinding | polishing process with respect to the foundry sand S can be adjusted by adjusting the quantity of the foundry sand S thrown in from the sand throwing-in part 514.

  The foundry sand that has been subjected to the second polishing step is conveyed to a classifier and performs the classification step (step S9). In the classification step, an air classifier that classifies with wind using the specific gravity difference is used, for example, divided into foundry sand having a center particle size of about 200 μm and foundry sand having a center particle size of about 100 μm. In addition, it may replace with a wind classifier and may implement a classification process using a sieve.

  The foundry sand divided in the classification process is respectively transported to a game-type magnetic separator equipped with an electromagnet of 5000 gauss or more, and a second magnetic separation process is performed (step S10). In the second magnetic separation process, the foundry sand in which the au- tic remains on the surface despite the first polishing process is removed by magnetic force. That is, the second magnetic separation process corresponds to the magnetic separation process referred to in the present invention. In addition, the auxetic scraped from the surface of the foundry sand by the first polishing step is also removed by the magnetic force. Even though the second polishing process is performed, even if fine powder having magnetism remains on the surface of the foundry sand, the fine powder can be removed by the second magnetic separation process.

  The foundry sand on which the second magnetic separation process has been performed is transported to the dust collector, and the dust collection process is performed (step S11). In the dust collection process, finally, fine impurities adhering to the foundry sand are removed once again.

  The foundry sand subjected to the dust collection process is stored in the storage tank as reclaimed sand (step S12). The recycled sand stored in the storage tank is mainly used as a core material manufactured by a shell mold method, a cold box method, a self-hardening mold manufacturing method, or the like.

  As described above, according to the method for reclaiming foundry sand of the present embodiment, fine powder adhering to the surface of foundry sand can be sufficiently removed. When the amount of fine powder in the recycled sand was measured by a turbidity test, the turbidity of the recycled sand obtained by carrying out the same process as the casting sand recycling method of the present embodiment except that the second polishing process was not carried out. While the degree was 200 to 400 NTU, the turbidity of the reclaimed sand obtained by carrying out the process of the method for reclaiming foundry sand according to this embodiment could be suppressed to 200 NTU or less.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope described in the claims. For example, in the method for reclaiming foundry sand according to the present embodiment, the second magnetic separation process is performed after the second polishing process. If the second polishing process is performed after the first polishing process is performed, the second polishing process is performed. A second magnetic separation step may be performed before the step. According to this, the second polishing step can be performed on the foundry sand after removing the auritic scraped from the surface of the foundry sand in the first polishing step in the second magnetic separation step.

  Furthermore, in the first polishing step, fine powder may be removed by blowing air to the foundry sand. In other words, the dust itself may be prevented from adhering to the foundry sand by blowing air when scraping away the auric from the surface of the foundry sand in the first polishing step. However, even if air is blown to the foundry sand in the first polishing step, it is difficult to completely prevent fine powder from adhering to the foundry sand, and the second polishing step is still necessary. If the fine sand is removed to some extent by blowing air to the foundry sand in the first polishing step, the load of the second polishing step is reduced.

3 First polishing machine 33 Grinding stone 34 Raising roller 5 Second polishing machine 52 Polishing drum 54 Blower

Claims (2)

A method for reclaiming sand that was recovered by separating the sand mold used for casting,
Roasting step of roasting the foundry sand and burning off the organic matter adhering to the foundry sand;
A first polishing step of scraping from the surface a coating containing magnetic hematite that has been formed on the surface of the foundry sand by performing the roasting step;
A second polishing step in which the surface of the foundry sand from which the coating has been scraped off from the surface is polished in a housing with a grinding ability lower than the grinding ability in the first polishing step;
The second polishing step is a step of peeling fine powder adhering to the surface of the foundry sand from which the coating has been removed by the first polishing step from the surface, and discharging the fine powder out of the casing by wind force. A method for reclaiming foundry sand.   2. The casting according to claim 1, further comprising a magnetic separation step of removing, by using a magnetic force, casting sand in which the film remains on the surface even though the first polishing step is performed. 3. How to recycle sand.